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Transportation Industry

Visualising trips and travel characteristics from GPS data

Road & Transport Research, Jun 2003 by Stopher, Peter R, Bullock, Philip, Jiang, Qingjian

Abstract

In the past three years, a number of attempts have been made to use Global Positioning System (GPS) devices to measure elements of person travel that have never been successfully measured by conventional interview and self-administered surveys. A key component of this application of GPS devices is to process the track points recorded, so as to produce maps and other visual representations of the travel conducted with the device. These maps and other visualisations of the travel are subsequently used in a prompted recall survey, to obtain additional data about the travel that cannot be measured by the GPS devices, such as travel purposes, number in the travelling party, and costs associated with the travel. Determining what constitutes a trip, and processing the data to produce a recognizable map of the travel is essential to the success of a prompted recall survey. In turn, the use of this type of survey avoids the need for survey subjects to enter data in a diary or electronic device during the travel-a task that is both burdensome and likely to be forgotten or omitted sufficiently often to negate most of the benefits of a GPS survey.

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This paper describes the use of the GPS devices in this type of survey, the paradigms used to convert the track points to coherent trips, examination and correction of the visualised travel, and methods used to prepare maps and other visual tools, which can be presented to subjects in a prompted recall survey. Methods to display the trips and other information that can be gained from alternative ways of presenting the data are also outlined in the paper. These include the ability to determine when a person travels in congested conditions, examination of delays at traffic lights and other controlled intersections, and identification of the locations of acceleration and deceleration episodes.

BACKGROUND

Over the past three years, there has been growing interest in measuring human travel patterns using Global Positioning System (GPS) or other similar semi-automatic devices (Draijer et al. 2000; Stopher and Bullock 2001). In most cases, individuals are recruited and asked to plug a GPS device into the car that the person usually drives. The GPS device then logs track points at a pre-specified interval, usually 1, 2, or 5 seconds. The device is capable of recording considerable quantities of data, which must subsequently be analysed so as to provide information useful to transport planners and others.

As discussed elsewhere (Stopher and Bullock 2001), there are generally two types of GPS data logging device used for research on household travel patterns. One type is a GPS device that is connected to a Personal Data Assistant (PDA) and which requires the respondent to enter data about each trip as the trip is started. This type of device was pioneered originally by the U.S. Federal Highway Administration, through work undertaken initially by Battelle (Wagner 1997). It has been developed further in recent work by Guensler and Wolf (1999). The second type of device is a 'passive' device that requires little or no intervention by the respondent, but which may require the use of a prompted recall survey, after the data have been collected and downloaded (Stopher and Wilmot 2000; Wolf et al. 2001; Stopher 2001). It is this type of device that is the major focus of this paper.

OBJECTIVES

The objectives of the work reported in this paper are to determine how to convert the data obtained from the GPS device into discrete trips, display these for a variety of potential uses, and also display other information of relevance that is collected by the device, such as speed or acceleration data. Although raw GPS track points can be viewed on most standard GIS packages, on-screen visual analysis is extremely time consuming for even small amounts of data. A number of applications for processing GPS data have been developed by the Institute of Transport Studies (ITS), Sydney, over the past two years.

In some applications, particularly those that ITS has been working on, there is a need to be able to append other data from a separate prompted recall survey that is conducted with the respondent after the GPS data have been collected and analysed. This requires that the data collected by the GPS are processed to provide a visual record that is meaningful to a respondent. Such a visual record can be either or both maps and tabular presentations of the data. If the only issue were to come up with a reasonable way to show a respondent a set of track points on a map, this would be relatively trivial. However, this is not the issue. Rather, the data need to be transformed from a set of track points collected over some period of time - ranging from a day to several weeks - to a set of line records, wherein each line represents a trip from an origin to a destination, and where the origins and destinations each represent locations where the respondent undertook some non-travel activity. In addition, a tabular presentation is needed that indicates the location and time of the trip start and end for each trip, the length of the trip in distance and time, and the day on which the trip was performed. Given that most trips are about 15 minutes in length, and if GPS data are collected at one-second intervals, there will be about 900 GPS track points for the average trip, and one day's worth of data from one vehicle will average somewhere in the region of 6000 to 10 000 data points. Processing this amount of data is not a trivial activity.

Transportation Industry

Visualising trips and travel characteristics from GPS data

Road & Transport Research, Jun 2003 by Stopher, Peter R, Bullock, Philip, Jiang, Qingjian

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